Differential-effect backing vat for coarse and fine particles

ABSTRACT

A method and apparatus for gravimetrically separating particles of different sizes and densities. A conical, liquid filled vat is closed at its smaller bottom opening by a rigid, flexibly mounted diaphragm and at its larger top opening by a flexibly mounted filter bed having a permeable bottom. The diaphragm and bed are rigidly connected and reciprocably driven along a vertical axis. The differential liquid flow promotes the migration of denser particles through the bed and into the vat.

O United States Patent [151 3,703,237 Cohen-Alloro et al. 1 Nov. 21,1972 [54] DIFFERENTIAL-EFFECT BACKING [56] References Cited VAT FORCOARSE AND FINE PARTICLES UNITED STATES PATENTS [72] Inventors: RichardCohen-Allow, Orleans; 2 gyc g Name; 2 344 094 I 3/1944 Kraut 209/455Grassaud, Orleans, all of France 2,743,816 5/1956 Medley ..209/455 [73]Assignee: Bureau De Recherches Geologiques 3,087,619 4/1963 Kraut..209/456 Et Minieres, Paris, France Primary ExaminerFrank W. Lutter[22] Fled: 1971 Assistant ExaminerRalph J. Hill [21] APPL No; 104,617Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT [30]Forms Apphcatlon Pnomy Data A method and apparatus for gravimetricallyseparating Jan. 7, 1970 France ..7000396 particles of different sizesand densities- A l, liquid filled vat is closed at its smaller bottomopening [52] US. Cl. ..209/426, 209/504, 209/500 by a rigid flexiblymmmted, diaphragm and at its [51] Int Cl Bosh 3/22 larger top opening bya flexibly mounted filter bed I having a permeable bottom. The diaphragmand bed [58] Field of Search ..209/425-427, 455, are rigidly connectedand reciprocably driven along a vertical axis. The differential liquidflow promotes the migration of denser particles through the bed and intothe vat.

6 Claims, 3 Drgwingjjigures DIFFERENTIAL-EFFECT BACKING VAT FOR COARSEAND FINE PARTICLES FIELD OF THE INVENTION This invention relates to amethod and an apparatus for the separation, in a moist medium, of agranular or pulverulent product whose constituents possess volume-weightdifferences, making it possible to promote this densimetric separationon the basis of particles with variable dimensions, even very fine ones,smaller than one one-hundredth of a micron.

BACKGROUND OF THE INVENTION Apparatuses of this type, known under thename of diaphragm vats or jigs, use the backing effect coming from thealternating movement of a membrane or a free piston. These apparatusesexist in different versions. Generally speaking, they transmit pulsingand suction motions which are propagated through the products to beseparated and they permit their densirnetric classification and theselective extraction of the heaviest particles, on the one hand, and ofthe lightest residual fraction, on the other hand.

This classification is furthermore promoted in most cases by thepresence of a medium with a suitable density, called bed, made up eitherof the product itself which has been calibrated in advance, or of aforeign material with a density or a nature that has been judiciouslyselected. This bed successively undergoes dilatations and retractions sothat, at the moment of its expansion, it can be traversed by thetheoretically densest particles, whereas the lightest particles of theupper layers are evacuated through the overflow of the particles.

The separation of the heavy particles and the light particles is thenaccompanied in the course of the dilatation of the bed. This dilatationis brought about by the rising movement of a volume of water pushed bythe mechanical backing system, whose movement goes in the same directionas that of the water current. An unfavorable effect of this risingmovement of the water is manifested upon the finest particles which,independently of their respective density, are moved toward the upperlayers and overflow the apparatus with the fraction of particlesconsidered to be light.

Such apparatuses are limited in terms of their utilization by theirimperfection which manifests itself not only on the level of the generaltechnical value of separation but also on the level of the grain sizestreated, whose densimetric classification decreases in efficiency,gradually, as the particles become finer. In effect, according to theregulating conditions adopted and the nature of the products treated,the conventional apparatuses furnish either a concentrate of heavyparticles with a high content but low recovery, constituted essentiallyof particles with large dimensions, as we have just said, or apreconcentrate of heavy particles with greater recovery but with a lowcontent because of the inevitable movement of fine, unclassifiedparticles which have filtered through the bed, thus contaminating thepreconcentrate. Furthermore, due to their mechanical design, theseapparatuses are inoperative when we want to treat a product made upexclusively of fine particles with dimensions of less than one-tenth mm.

In this case, we generally run into difficulties in starting thefluidization due to the formation of an impermeable surface crust. Thiscrust affords no free passage toward the bottom of the feed product and,through its own movement, disturbs the gravimetric classification of thesubjacent particles. The unclassified assembly of these particles windsup by traversing the bed and-contaminating the preconcentrate. In aneffort to reduce this inconvenience somewhat, certain apparatuses add,to the principal rising water current, a secondary water current whichcompensates for the suction and which is designed to prevent theformation of the crust. But this produces a permanent upward movement ofthe fine particles, independently of their respective densities.

SUMMARY OF THE INVENTION According to this invention for the gravimetricseparation of granular or pulverulent materials in the form of coarseparticles or in the form of fine particles smaller than one-tenth mm, orin the form of any kind of mixture of fine and coarse particles, we pourthe mixture to which recoverable and recyclable particles, with a grainsize greater than that of the products to be treated, can be added, insuch a manner as to produce an extended layer of grains in a basket witha permeable bottom, attached on an elastic support connected to thewalls of a vat filled with a liquid fluid. We then subject said basketto an alternate vertical movement, synchronized with conventional meansfor providing alternate movements of the liquid contained in the vat,such as a piston or a diaphragm.

Experience has shown that such a method offers the considerableadvantage of eliminating not only the movement of the fine undesirableparticles, which soil the dense products collected, through suction, butalso the rejection of the fine particles of the dense products whichwere lost with the earlier apparatuses where the suction effect had tobe systematically compensated by a supply of liquid from the outsidethat would oppose the descending movement of the water in the vat. Inthe method involved in this invention, we get, on the contrary, aremarkable sedimentation of dense products during the rising current ofthe liquid through the basket, a period of time in whose course thebasket sinks into the liquid, causing the perfect fluidization of thebed and the materials to be treated. The apparatus according to themethod recommended here employs a backing movement in a directionopposite to the one of the fluid which runs across the bed.

Furthermore, in the method of this invention the volume of liquidpassing through the bottom of said basket, during its alternatingmovement synchronized with the alternating movement of the membrane orthe piston that moves the liquid along, is greater than the volume ofwater displaced by said diaphragm or piston, whereas the movements ofthe basket and the piston have the same amplitude in order to produce adifferential effect due to the inequality of the cross-sections of thebases of the vat, the upper base having a larger cross-section than thelower base. This method not only makes it possible to simplify thebasket move ment control mechanisms, since it suffices to have a simplemechanical connection between the basket and the piston, but also makesit possible to improve the regularity of the passage of the waterthrough the basket and the separation in a fluidized bed in ahomogeneous manner.

Further according to this invention, the movement of the basket isabruptly speeded up at the beginning of its descent, whereas the wave ofthe liquid above the materials contained in the basket is regulated by asystem of fixed vertical walls acting as breakwaters. The regulation ofthe wave of the liquid synchronized with the abrupt descent of thebasket results in liberating all of the grains of their support andthese grains react differently in the rising water current which isuniform as a function of their volumes and their respective densities.Experience has shown that it is then very easy not only to separate thematerials made up of particles with greatly varying dimensions but alsoto separate materials made up of very fine particles and with dimensionsless than one-tenth of a mm. This result, which could not be obtainedwith the earlier processes, stems from the free sedimentationaccomplished in a very short time, and continues throughout the entirefluidization of the bed and of the product to be treated without adisturbance of the liquid zone above the bed.

The method of this invention is improved even further by combining themovement of raising the basket with the operation of establishingcontact between the vat, at a level situated between the basket and thepiston, and an open liquid tank and by coupling the descending movementof the basket with the cutting of said connection, accompanied by aslight progressive and momentary withdrawal of the water below thebasket. This enables us to eliminate the slight suction effect whichoccurs as a result of the rise of the basket and which would havebrought about, if not the movement of the fine, low-density particles,since the suction effect produced by the process involved in thisinvention no longer has the same intensity as the suction effectsproduced by the earlier apparatuses, then at least a slowdown in theseparation. In this way we can improve the speed of separation ofmaterials treated while still retaining the purity of materialsselected, especially in the case of a mixture of particles with varyinggrain sizes. n the other hand, a supply of liquid, designed tocounteract the suction produced in the earlier apparatuses, employing amethod consisting in pushing and aspirating a volume of water by thedirect effect of a piston or a diaphragm across the layer of products tobe fluidized, brings about a disturbance of the medium since the supplyof water, if it is to be effective, must oppose the descending currentproduced by the withdrawal of the piston, thus bringing about therejection of the light particles through the overflow of the bed. Theapplication of the method with differential effect, as involved in thisinvention, on the contrary only very slightly slows down the thrusteffect of the liquid in the course of the descent of the basket andprevents the beginning of suction during the thrust of the water by thepiston and the beginning of the rise of the basket by establishingcontact between the vat and an open tank containing liquid. In this waywe can prevent any kind of disturbances which were due to the more orless intensive countercurrent created in the earlier compensationsystems. r

The apparatus for implementing the process of this invention involves avat having an upper opening with a cross-section larger than that of thelower opening, a

mobile part, connected along a strictly vertical axis, in a sealed andelastic fashion, to said lowering opening, a device for the alternatingmovement of said mobile part, a basket support of solid particles to beinvolved in fluidization, said basket having a horizontal bottom whichis permeable to the passage of liquid filling said vat, as well as tothe dense particles separated in the course of the operation, a meansfor elastic and sealed attachment connecting said basket. to theperiphery of said upper opening of said vat, and internal means makingthe mobile part into one piece with said basket, said vat beingsurrounded by a tank whose liquid covers said basket.

in this way we get a very simple apparatus in which the liquid volumepassing across the surface of the bottom of the basket in the course ofits rising or descending movement is greater than that displaced by themobile part.

This apparatus further involves a system of breakwater walls plungedinto the upper zone of the fluid, a charging hopper along the axis ofthe vat, and at least one axis opening leading to the wall of the vat ata level between the mobile part and the basket, said opening beingconnected by a flexible and deformable conduit to a tank equipped with aliquid inlet and a float valve regulating the passage of the liquidcontained in the vat toward said tank.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features of theinvention will emerge from the following specifications given here withreference to the attached drawings which, by way of nonrestrictiveexample, represent one apparatus using the densimetric separationprocess through backup movement in the opposite direction to that of thefluid traversing the bed.

In the drawings:

FIG. 1 is an elevation and cross-section view of an apparatus of thisinvention, 7

FIG. 2 is a plan view of FIG. 1, and

FIG. 3 is a diagram showing the volume difl'erences produced by thedisplacements of the mobile parts of the apparatus shown in FIG. 1. 1

In FIG. 1 we see a frame 1 to which is attached, in a rigid fashion, thecircular body 2 of the backup vat. A circular vat with an inclinedbottom 3 is attached to frame 1 and vat 2. it carries an emptying memberin its lower portion 4 which can be provided with an automatic openingand closing device 22 and an overflow 20 in its upper portion.

The lower portion of vat 2 is equipped with a mobile part 5 that acts asa piston or diaphragm. It is connected to vat 2 by an elastic andflexible device 6 and at its lowest point has an evacuation conduit 21for the evacuation of the concentrates made up of dense particles thathave traversed the basket.

A basket 7 is connected to the upper portion of vat 2 by another elasticand flexible device 8. in the example shown, basket 7 has a cylindricalshape. It is equipped with a perforated bottom 9 which supports the bedand substance, such as sheet metal, perforated sheet metal,

a bar-grid, porous bottoms made of metal or plastic material, flexibleor rigid, etc. It can also be made by any combination of these elements.The filter bed, which is designed to permit the preferential passage ofthe heavy particles, is shown at 11 and the product being treated isshown at 12.

Basket 7 is connected, by means of its bottom 9, to piston 5 throughcrosspieces 10.

A breakwater device 13 is attached to vat 3 by a rigid support 14 whichholds the charge hopper 15.

The mobile part 5 of vat 2 is guided vertically by rods 16 equipped withrollers 29 that ride on vertical tracks of frame 1.

An alternating movement is imparted to part 5 by lever 17 articulated at30 upon frame 1. A cam 18, with a profile specially developed so as toreveal an abrupt profile variation in order to bring about, in eachcycle, the abrupt displacement of the basket, is made to rotate by amotor group 19 and contacts the lever 17 through a roller 31 mounted ona support 32 which can be moved along lever 17. The motor group 19preferably involves a speed changer so as to furnish the desired cadencefor the movement of the mobile part.

An auxiliary moderating device, shown by tank 23, can be connected tovat 2 by means of a flexible, expansible sleeve 28. The tank 23 containsan enclosure 24 comprising a basket 25 and a lid 26 equipped with anopening 26a. A float 27 moves in the basket 25.

In the plan view in FIG. 2, we again find vat 3, breakwater 13, hopper15, as well as their supports 14, which connect them to vat 3. We alsosee moderating device 23, the lid 26 of the enclosure 24, the float 27and the flexible connecting sleeve 28. FIG. 2 shows the assembly of themotor group made up of motor 19a, speed changer 19b, and reducing gear19c, controlling the cam 18 which activates the lever 17.

In order to bring out the liquid volumes V and v, which are moved,respectively, by the movement of basket 7 and the mobile part 5, actingas a piston, we have shown in FIG. 3 only the mobile assembly made up ofbasket 7 and piston 5, controlled by lever 17. In the drawing we can seethat, because of the amplitude H of the movement, the volume V, producedby the displacement of the basket 7, is greater than the volume v,produced by the movement of the piston 5. From this it results that,during the descent of the piston 5, the basket 7 is subjected to anupward pulsation of the fluid, with the fluid volume traversing thepermeable bottom of basket 7 being equal to V v.

The apparatus shown in FIG. 3 can also be used with the moderatingdevice 23 in FIG. 1. We can see that, contrary to the earlier devices,the rise of the piston does not produce a pulsation of the liquid towardthe top, through basket 7, but rather a relatively slow suc tion becauseof the shape given to cam 18. In the course of this period, there is nodisturbance of the bed, and the dense materials here gather at thebottom of the bed while passing through the permeable floor. As wereverse the movement, the basket 7 and piston 5 are abruptly returned totheir original position where they remain for an interval of time duringwhich the free sedimentation of the particles occurs.

In order to increase the output and the separation speed when thematerial to be treated contains particles with varying grain sizes, weuse the regulating device shown in FIGS. 1 and 2, as we saw earlier.

During the rise of basket 7 and mobile part 5, the start of suction,produced by these displacements, is immediately reduced by the inflow ofliquid contained in tank 23 and in the connecting channel leading to vat2. Sleeve 28 is deformed, responding immediately to the pull of theliquid inside vat 2. This liquid displacement brings about the openingof float valve 27 which leaves its place 26a thus providingcommunication between tank 23 and vat 2.

Inversely, during pulsation, that is to say, during the abrupt descentof the basket, a portion of the impulse is absorbed by the inflation ofextensible sleeve 28, thus giving greater mechanical flexibility to theapparatus and better fluidization since no disorderly disturbance of thebed can occur.

Device 23 may be regulated in terms of height so as to furnish a volumeof liquid suitable for vat 2. When valve 27 is used, we compensate theloss of liquid by direct supply represented schematically at 33.

We eliminate any parasite wave effect by using a breakwater 13 whosewalls are submerged in the upper zone of the liquid. By way of example,the breakwater may be made up of walls in the prolongation of the wallsof the basket 7. We thus promote the free sedimentation of fineparticles in suspension in the fluid.

The movement of the products to be treated is performed with the help ofa central hopper l5, permitting the deposit of materials to be treatedin the center and above the bed 11, that is to say, in the center of thesurface layer 12.

The movements of the fluid, as well as those of basket 7, bring aboutthe radial displacement of the particles which, during this action,undergo the desired densimetric classification effect. At the end of therun, the light products overflow at the periphery of basket 7 and fallinto the recovery vat 3 from which they flow along the slanted bottom ofthis tank in order then to be evacuated at 4, either continuously orperiodically, by a valve 22.

According to one variation, we can use the regulating device without thevalve 27. The pulsation effect is then reduced and it diminishes, justlike the suction effect. The fluid contained in vat 2 is then inpermanent communication with vat 23 of the regulating device. There isthen a tendency toward the establishment of a constant level between thewater level in vat 3 and that in tank 23.

Experiments have shown that this manner of utilization, without a floatvalve, is particularly well suited to the treatment of extra-fineparticles, smaller than onetenth mm. In the case of coarse particles,whose dimension is, for example, greater than 1 mm, the apparatusfurnishes high-yield separation without the moderating device.

We claim:

1. An apparatus for the gravimetric separation of granular orpulverulent materials, comprising:

a. a vertically oriented container having top and bottom openings, thetop opening having a larger cross-sectional area than the bottomopening,

b. a movable member sealingly connected by elastic means to the bottomopening,

c. driving means for imparting a reciprocating vertical movement to themovable member,

d. a basket member having a horizontal floor that is permeable to bothliquid filling the container and to particles to be separated from thegranular or pulverulent material,

e. elastic means for sealingly connecting the basket member to the topopening of the container,

f. means rigidly connecting the basket member to the movable member formovement therewith, and

g. a tank surrounding the container and containing liquid at a levelsufficient to cover the basket member.

2. An apparatus as recited in claim 1 further com-- prising:

a. a breakwater wall secured to the tank and suspended in the liquidabove the basket member, the basket member having an outer wall alignedwith the breakwater wall,

. a charging hopper for supplying granular or pulverulent material to beseparated to the basket member,

. a second liquid container connected to the vertically orientedcontainer at a position between the basket member and the movable memberby a flexible and deformable conduit, and valve means within the secondcontainer for regulating the flow of liquid into the vertically orientedcontainer.

3. An apparatus as recited in claim 1 wherein the driving means includesa cam profiled to cause a gradual rise and a rapid fall of the movablemember.

4. An apparatus as recited in claim 1 wherein:

a. the movable member has an inclined bottom with an opening therein forthe discharge of dense particles that have been separated out throughthe basket member, and

b. the tank has an inclined bottom with an opening therein for thedischarge of dense particles that member sealingly and flexiblyconnected to the bottom opening of the container, said bottom openinghaving a smaller cross-sectional area than said top opening, and a 0.simultaneously imparting said reciprocating vertical motion to thebasket member in synchronization with the motion imparted to the rigidmember. 6. A method as recited in claim 5 wherein the reciprocatingvertical motions are equal in amplitude and are characterized by agradual rise and a rapid fall.

1. An apparatus for the gravimetric separation of granular orpulverulent materials, comprising: a. a vertically oriented containerhaving top and bottom openings, the top opening having a largercross-sectional area than the bottom opening, b. a movable membersealingly connected by elastic means to the bottom opening, c. drivingmeans for imparting a reciprocating vertical movement to the movablemember, d. a basket member having a horizontal floor that is permeableto both liquid filling the container and to particles to be separatedfrom the granular or pulverulent material, e. elastic means forsealingly connecting the basket member to the top opening of thecontainer, f. means rigidly connecting the basket member to the movablemember for movement therewith, and g. a tank surrounding the containerand containing liquid at a level sufficient to cover the basketmember.
 1. An apparatus for the gravimetric separation of granular orpulverulent materials, comprising: a. a vertically oriented containerhaving top and bottom openings, the top opening having a largercross-sectional area than the bottom opening, b. a movable membersealingly connected by elastic means to the bottom opening, c. drivingmeans for imparting a reciprocating vertical movement to the movablemember, d. a basket member having a horizontal floor that is permeableto both liquid filling the container and to particles to be separatedfrom the granular or pulverulent material, e. elastic means forsealingly connecting the basket member to the top opening of thecontainer, f. means rigidly connecting the basket member to the movablemember for movement therewith, and g. a tank surrounding the containerand containing liquid at a level sufficient to cover the basket member.2. An apparatus as recited in claim 1 further comprising: a. abreakwater wall secured to the tank and suspended in the liquid abovethe basket member, the basket member having an outer wall aligned withthe breakwater wall, b. a charging hopper for supplying granular orpulverulent material to be separated to the basket member, c. a secondliquid container connected to the vertically oriented container at aposition between the basket member and the movable member by a flexibleand deformable conduit, and d. valve means within the second containerfor regulating the flow of liquid into the vertically orientedcontainer.
 3. An apparatus as recited in claim 1 wherein the drivingmeans includes a cam profiled to cause a gradual rise and a rapid fallof the movable member.
 4. An apparatus as recited in claim 1 wherein: a.the movable member has an inclined bottom with an opening therein forthe discharge of dense particles that have been separated out throughthe basket member, and b. the tank has an inclined bottom with anopening therein for the discharge of dense particles that have movedacross the top of and overflowed the basket member.
 5. A method for thegravimetric separation of granular or pulverulent materials, comprising:a. forming a layer of granular or pulverulent materials in a basketmember having a permeable bottom and being sealingly and flexiblyconnected to the top opening of a vertically oriented, liquid filledcontainer, b. imparting a reciprocating vertical motion to a rigidmember sealingly and flexibly connected to the bottom opening of thecontainer, said bottom opening having a smaller cross-sectional areathan said top opening, and c. simultaneously imparting saidreciprocating vertical motion to the basket member in synchronizationwith the motion imparted to the rigid member.